| 摘要 |
PURPOSE:To generate a character signal even when a video signal is absent by using a signal absence detecting circuit to detect the presence and absence of the video signal, a signal changing-over circuit controlled by the circuit and a synchronizing signal generating circuit connected to a character signal generating circuit at the time fo the signal absence. CONSTITUTION:When a video signal is not inputted to an input terminal 1, a signal changing-over circuit 7 is changed-over to a B side by a signal absence detecting circuit 3. Consequently, to a character signal generating circuit 8, a synchronizing signal 12 prepared by a synchronizing signal generating circuit 5 is inputted and a stable character signal 13 is generated. The synchronizing signal 12 enters a replacing circuit 9 through a level shifting circuit 6 and a signal changing-over circuit 7. When the character signal is absent, an output 14 of the replacing circuit 9 comes to be one black color. Consequently, when the video signal is absent, the signal waveform to overlap a white character to a black background is obtained.
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